\subsection{Grasp Task}
\label{grasp}

\paragraph{Completion Time}

On the time to complete a trial,
a \LMM \ANOVA with by-participant random intercepts indicated two statistically significant effects:
\factor{Positioning} (\anova{4}{3990}{13.6}, \pinf{0.001}, see \figref{results/Grasp-CompletionTime-Location-Overall-Means})
and \factor{Target} (\anova{3}{3990}{18.8}, \pinf{0.001}).
\level{\level{Opposite}} was faster than \level{Fingertips} (\percent{+19}, \pinf{0.001}), \level{Proximal} (\percent{+13}, \pinf{0.001}), \level{Wrist} (\percent{+14}, \pinf{0.001}), and \level{Nowhere} (\percent{+8}, \p{0.03}).
\level{Nowhere} was faster than \level{Fingertips} (\percent{+11}, \pinf{0.001}).
\level{RF} was faster than \level{RB} (\pinf{0.001}), \level{LB} (\pinf{0.001}), and \level{LF} (\pinf{0.001});
and \level{LF} was faster than \level{RB} (\p{0.03}).

\paragraph{Contacts}

On the number of contacts,
a \LMM \ANOVA with by-participant random intercepts indicated two statistically significant effects:
\factor{Positioning} (\anova{4}{3990}{15.1}, \pinf{0.001}, see \figref{results/Grasp-Contacts-Location-Overall-Means})
and \factor{Target} (\anova{3}{3990}{7.6}, \pinf{0.001}).
Fewer contacts were made with \level{Opposite} than with \level{Fingertips} (\percent{-26}, \pinf{0.001}), \level{Proximal} (\percent{-17}, \pinf{0.001}), or \level{Wrist} (\percent{-12}, \p{0.002});
but more with \level{Fingertips} than with \level{Wrist} (\percent{+13}, \p{0.002}) or \level{Nowhere} (\percent{+17}, \pinf{0.001}).
It was also easier on \level{LF} than on \level{RB} (\pinf{0.001}), \level{LB} (\p{0.006}), or \level{RF} (\p{0.03}).

\paragraph{Time per Contact}

On the mean time spent on each contact,
a \LMM \ANOVA with by-participant random intercepts indicated two statistically significant effects:
\factor{Positioning} (\anova{4}{3990}{2.9}, \p{0.02}, see \figref{results/Grasp-TimePerContact-Location-Overall-Means})
and \factor{Target} (\anova{3}{3990}{62.6}, \pinf{0.001}).
It was shorter with \level{Fingertips} than with \level{Opposite} (\percent{+7}, \p{0.01}).
It was also shorter on \level{RF} than on \level{RB}, \level{LB} or \level{LF} (\pinf{0.001});
but longer on \level{LF} than on \level{RB} or \level{LB} (\pinf{0.001}).

\paragraph{Grip Aperture}

On the average distance between the thumb's fingertip and the other fingertips during grasping,
a \LMM \ANOVA with by-participant random intercepts indicated two statistically significant effects:
\factor{Positioning} (\anova{4}{3990}{30.1}, \pinf{0.001}, see \figref{results/Grasp-GripAperture-Location-Overall-Means})
and \factor{Target} (\anova{3}{3990}{19.9}, \pinf{0.001}).
It was longer with \level{Fingertips} than with \level{Proximal} (\pinf{0.001}), \level{Wrist} (\pinf{0.001}), \level{Opposite} (\pinf{0.001}), or \level{Nowhere} (\pinf{0.001});
and longer with \level{Proximal} than with \level{Wrist} (\pinf{0.001}) or \level{Nowhere} (\pinf{0.001}).
But, it was shorter with \level{RB} than with \level{LB} or \level{LF} (\pinf{0.001});
and shorter with \level{RF} than with \level{LB} or \level{LF} (\pinf{0.001}).

\begin{subfigs}{grasp_results}{Results of the grasp task performance metrics for each vibrotactile positioning.}[
    Geometric means with bootstrap \percent{95} confidence and Tukey's \HSD pairwise comparisons: *** is \pinf{0.001}, ** is \pinf{0.01}, and * is \pinf{0.05}.
  ][
  \item Time to complete a trial.
  \item Number of contacts with the cube.
  \item Time spent on each contact.
  \item Distance between thumb and the other fingertips when grasping.
  ]
  \subfig[0.24]{results/Grasp-CompletionTime-Location-Overall-Means}
  \subfig[0.24]{results/Grasp-Contacts-Location-Overall-Means}
  \subfig[0.24]{results/Grasp-TimePerContact-Location-Overall-Means}
  \subfig[0.24]{results/Grasp-GripAperture-Location-Overall-Means}
\end{subfigs}